Tenter frames are commonly employed in web treating processes of the textile and thermoplastic film manufacturing industries.
Such frames consist of a multiple number of guide rails pivotally connected together. Each guide rail has opposite and parallel guide surfaces which provide a working surface and a return surface for an endlessly moving tenter clip chain.
Each tenter frame consists of two oppositely located guide rails. Two saddles, one for each guide rail, are slidably mounted upon a cross member of the machine frame. A shaft having a left hand thread and a right hand thread is rotatably mounted to the cross member. The two saddles are, respectively, connected to the left hand thread and the right hand thread. Rotation of the shaft moves the two saddles toward and away from each other to decrease or increase the distance between the two oppositely located saddles and guide rails. This movement causes adjacent guide rails to pivot around a connecting pivot pin and thereby increase or decrease the gap between adjacent guide rails.
The tenter clips pivotally connected together form a tenter chain. The clips ride against the working surfaces and return surfaces of the guide rails which form a guide path. The tenter clips located in the oppositely located guide rail paths grasp the edges of the webs being treated and convey these webs across the tenter frame.
Thermoplastic film is commonly stretched in the transverse direction by use of such tentering means. The tenter clips passing from one guide rail section to the pivotally connected adjacent guide rail section encounter a gap between adjacent guide rail sections. This gap causes the tenter clip to jar, jump and shockingly abut the opposite edges of the gap and in general hinder the smooth gentle passage of the tenter clips around the, respective, guide rail paths.
The jarring causes a ripple and thereby the destruction of a section of the thermoplactic film web. The jumping hinders the speed of movement of the tenter chain in the guide path. The shocking physically destroys both the guide path and the tenter clips and significantly increases the requirement of the driving motor. The gap also causes the tenter chain to vibrate. The result is nonuniformity of product, web breaks, and a major cause of equipment failure.